1. Field of the Invention
The present invention relates to a spindle motor and a hard disc drive including the same.
2. Description of the Related Art
A hard disc drive (HDD), an information storage device, is a device for reading data stored on a disc or writing data to a disc with a read/write head.
A hard disc drive requires a disc driving device for driving a disc, and a small spindle motor is used in the disc driving device.
Such a small spindle motor employs a fluid dynamic pressure bearing assembly, in which a lubricating fluid is interposed between a shaft, a rotary member of the fluid dynamic pressure bearing assembly, and a sleeve, a fixed member of the fluid dynamic pressure bearing assembly, and the shaft is supported by fluid pressure generated in the lubricating fluid.
Also, a rotor hub, rotated together with the shaft and having a recording disc mounted thereon, is mounted on an upper side of the shaft. The rotor hub is fixedly coupled to an upper portion of the shaft and has a disc-like shape spread in a radial direction with the shaft as the center. Thus, a lubricating fluid is interposed between an upper surface of the sleeve and the rotor hub.
In the related art, a hard disc drive (HDD) used for a mobile device has a thickness of 9.5 mm, while an HDD used for a server has a thickness of 15 mm, so a spindle module installed therein may be formed to extend in an axial direction to a degree. Namely, since a bearing span of a vertical radial bearing is sufficiently secured, even in the case that a rotary member of the spindle motor is sloped to one side by external force or other force while rotating, the rotary member does not have a difficulty in being returned to its original position by the hydrodynamic condition of the vertical radial bearing formed between the shaft and the sleeve.
However, recently, as the size of electronic devices has been reduced, a thickness standard of a hard disc drive used in electronic devices is required to be 5 mm or smaller, and thus, a spindle motor used therein is formed to be significantly short in an axial direction.
Thus, as the length of the shaft is reduced relative to the related art spindle motor, it is difficult to form fluid dynamic pressure for returning the rotary member of the spindle motor to its original position when sloped to one side. Namely, a bearing span of the vertical radial bearing is too short to secure sufficient slope rigidity.
As a solution to a lack of slope rigidity according to a radial bearing, a method of increasing bearing rigidity by generating strong fluid dynamic pressure by reducing a bearing clearance, i.e., a gap between the shaft and the sleeve may be considered. In this case, however, if dynamic pressure is increased, frictional loss is increased, eventually leading to an undesirable increase in power consumption.